Ischnochiton muscarius (Reeve, 1847)

Figures 2C–F, 5E–K, 6A–I

Distribution. Isla El Venado, Sonora to La Ventosa, Oaxaca, including Isla Socorro, Revillagigedo, México (Kaas & Van Belle 1990).

Type specimens. Unascertained, according to Kaas & Van Belle (1990) and Ferreira (1983b).

Type Locality. Unknown, maybe Lower California (according to Kaas & Van Belle 1990) .

Material examined. 169 specimens, maximum size of 30.4 mm long, 15.5 mm wide. L (n=15); B (n=17); G (n=10); H (n=9); D (n=8); M (n=16); K (n=11); P (n=10); U (n=9); Q (n=12); S (n=6); E (n=5); F (n=11); J (n=7); N (n=5); A (n=10); I (n=8).

Habitat. This species is usually found in large aggregations on smooth rocks and with crustose algae. It is particularly abundant in shallow subtidal (2–4 m), buried on small to medium rocks. Juvenile specimens (between 8–16 mm of body length) occur in subtidal to 10 m on small rocks buried in sand. It was collected with C. lurida, T. forbesii and S. limaciformis .

Remarks. This species was one of the most abundant species found during this study comprising 26% of the total specimens collected (Table 2). Color varies from olive green, brown, yellow, or gray (Figs. 2C–F); frequently the whole tegmentum area of the intermediate valves (IV or V) is dark green or black in color. We also observed dark, fine longitudinal bands in the lateral areas, directed concentrically to the apex; this pattern was also observed in specimens from Nayarit and Mazatlán. However, chitons from southern areas in Oaxaca (e.g., CNMO 5662) lack the characteristic chessboard pattern located on head and tail valve (Fig. 20K), as well as the olive-green or dark brown dots on the central areas.

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TABLE 2. (Continued)

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TABLE 3. (Continued)

Family Callistoplacidae Pilsbry, 1893